Systems of electrical, electromagnetic or magnetic transmission-lines or ‘delay-lines’ (electrical, electromagnetic or magnetic transmission elements with a length that is at least a substantial fraction of the wavelength of the highest frequency component of an electrical, electromagnetic or magnetic signal that propagates along them) are found in various forms in engineering, scientific, and industrial instrumentation. Electrical delay-lines are in very widespread use; most commonly in the context of simple ‘interconnects’ i.e. channels to support communication between functional lumped electrical (or part-electrical) components. Apart from matching applications, the electrical properties particular to delay-lines are rarely exploited; indeed there is a widespread misconception that the incorporation of a section or sections of delay-line into an electrical system must be fundamentally deleterious to its overall performance. Moreover, the potential of certain electromagnetic and/or magnetic delay-line systems—in particular spin-wave delay-line systems—to form the basis of devices and systems with novel functionalities provided by their particular effective impedance properties remains largely unexplored.